Portable battery-powered radio products, such as cellular phones, are becoming increasingly compact as a result of the development of smaller and longer-lasting batteries. These batteries, however, typically do not have high output voltages. For instance, lithium batteries, commonly used in many cellular phone products, have an output voltage around 3.6 volts per cell. Such an output voltage, while useful in many applications, may not be sufficient for power amplifiers which typically require a higher supply voltage for optimum performance. Furthermore, different components within the portable radio products may require different power supply voltages for optimal performance. Thus, a voltage converter is often used to transform the battery voltage to other voltages as required by the specific applications.
One major drawback of using a voltage converter in portable radio products, however, is power dissipation. The problem is exacerbated in portable or mobile radio products where battery capacity is limited. Thus, even a low level of dissipation by the voltage converter causes a significant decrease in battery life. In order to decrease power dissipation, switching voltage regulators are typically used as voltage converters. A switching voltage regulator is well known in the art and generally comprises a pass transistor which oscillates between cutoff and saturation. Thus, the pass transistor acts as a switch that is rapidly being turned on and off. The rapid switching, coupled with a network of inductors and capacitors, boosts up or bucks down an input voltage. A text-book example of such a switching voltage regulator can be found in Greenfield, J., Practical Transistors and Linear Integrated Circuits, pp. 505-515, John Wiley & Sons, Inc., 1988.
In order to further minimize power dissipation, highly complicated voltage regulators using state of the art components and designs have been devised. However, the level of dissipation remains relatively high. Indeed, in prior art battery-operated portable transceivers, the maximum overall transmitter power efficiency is limited to roughly 40% when the transmitter transmits at its maximum output power. A significant amount of energy is consumed by the switching voltage regulator. When the transmitter transmits at lower power levels, the overall transmitter power efficiency becomes even lower. Thus, what is needed is an apparatus for and method of increasing the efficiency of the voltage converters such that a minimum amount of energy is dissipated in the voltage converters. What is further needed is an apparatus for and method of adaptively controlling power supplied to power amplifiers and signal transmitters in battery-operated transceivers to achieve maximum efficiency.
Accordingly, the present invention provides a system for and method of minimizing power dissipation of voltage converters in radio products. The present invention also provides a mechanism for providing the minimum necessary power to the transceiver by adaptively providing a high power supply voltage and a low power supply voltage to the transceiver. Further, the present invention provides a mechanism and method for controlling a switching voltage regulator to supply a low power supply voltage at maximum efficiency. These and other advantages of the present invention not specifically mentioned above will become clear within discussions of the present invention presented herein.